@borderColor: #01d1fb;  //角的颜色
@borderWidth: 3px;  //角的宽度
@borderGap: 1px;    //角距离矩形边角的距离
@borderLength: 20px;    //角的x轴y轴长度
html, body {
    height: 100%;
}
body {
    background: #030813;
}

@keyframes flashing {
    0% {
        box-shadow: none;
    }
    50% {
        box-shadow: 0 0 17px 1px #4746a2;
    }
    100% {
        box-shadow: none;
    }
}
.rect {
    position: relative;
    width: 40%;
    height: 40%;
    border: 1px solid #0c5371;
    margin: 0 auto;
    transform: translateY(50%);
    animation: flashing 2s ease infinite;
    .cornor {
        position: absolute;
        border-style: solid;
        border-color: @borderColor;
        width: @borderLength;
        height: @borderLength;
    }
    .cornor:nth-child(1) {
        left: -@borderGap;
        top: -@borderGap;
        border-width: @borderWidth 0 0 @borderWidth;
    }
    .cornor:nth-child(2) {
        right: -@borderGap;
        top: -@borderGap;
        border-width: @borderWidth @borderWidth 0 0;
    }
    .cornor:nth-child(3) {
        right: -@borderGap;
        bottom: -@borderGap;
        border-width: 0 @borderWidth @borderWidth 0;
    }
    .cornor:nth-child(4) {
        left: -@borderGap;
        bottom: -@borderGap;
        border-width: 0 0 @borderWidth @borderWidth;
    }
}